Francisco A. Bonilla holds both M.D. and Ph.D. (Immunology) degrees. Following clinical training in Pediatrics, and a fellowship in Allergy/Immunology at Children's Hospital, Boston, he has recently been appointed to the faculty of the Division of Immunology at this institution. Dr. Bonilla now plans to continue as a Scientist Physician performing basic Immunology research, with the eventual goal of becoming an independent investigator. Dr. Bonilla's work will be carried out within the research facilities of the Division of Immunology of Children's Hospital. A large body of literature strongly suggests that the lymphocyte surface marker CD7 has an important role in the development and function of a number of leukocyte lineages. However, the ligand for CD7 and its signaling pathways remain unknown. We will use the method of targeted gene disruption to create mice lacking CD7. This will provide a system in which to clearly define the importance of CD7 in the development and function of the cells which express it CD7-deficient mice will be studied with respect to the representation of lymphocyte subpopulations in primary and secondary lymphoid tissues by flow cytometry, and immunohistochemical methods. They will be challenged in vivo with several antigens and their antibody responses assessed. They will also be subjected to a comprehensive battery of in vitro tests of T cell, B cell, and natural killer cell function. We will also study the interaction of the intracellular portion of CD7 with signaling pathways. We will create a number of hybrid constructs consisting of the external portion of the human CD8 molecule joined to the cytoplasmic domain of human CD7. The CD7 domain will be subjected to various mutations and deletions; cells transfected with these constructs will be studied with respect to several biological effects associated with CD7 ligation. In addition, we will employ the yeast two hybrid system to identify proteins associated with the intracellular domain of CD7. Interacting proteins will be cloned and sequenced. We will attempt to determine their potential roles in signaling through structural comparisons with known proteins, as well as by analyzing phosphorylation patterns following cellular stimulation.